10376 14a

Chapter

14
Synthetic Polymers

Hasan A. Al-Muallem
14.1

Basic Concepts and Definitions

511

14.2

Classification of Polymers

513

14.3

Polymers Industry

520

14.4

Polymer Structure

520

14.5

Polymer Structure-Property Relationships

541

14.5.1

Thermal properties

541

14.5.2

Mechanical properties

546

14.5.3

Solubility

548

14.5.4

Viscosity

14.6

Rheology

14.7

Molecular Weight of Polymers

14.8 The Synthesis of High Polymers

14.9

554
556
560
564

14.8.1

Condensation or step-reaction polymerization

569

14.8.2

Addition or chain-reaction polymerization

572

14.8.3

Free radical polymerization

573

14.8.4

Ionic polymerization

582

Polymerization Techniques

594

14.10

Copolymerization

600

14.11

Modification of Synthetic Polymers

607

14.12

Degradation, Stability, and Environmental Issues

611

14.13

Polymer Additives

616

References

618

14.1

Basic Concepts and Definitions

A polymer is a giant molecule made up of a large number of repeating
units joined together by covalent bonds. The simple compounds from
which polymers are made are called monomers. The word polymer is
derived from the Greek words poly (many) and meros (parts). Polymer


molecules have molecular weight in the range of several thousands or
more, and therefore, are also referred to as macro molecules. This is
illustrated by the following equation, which shows the formation of the
polymer polystyrene.

Styrene
(monomer)

Polystyrene
(polymer)

(D

The styrene molecule is the monomer, and the resulting structure,
enclosed in square brackets, is the polymer polystyrene. The unit in
square brackets is called the repeating unit. Some polymers are derived
from the mutual reaction of two or more monomers. For example,
poly(hexamethylene adipamide) or nylon-6,6 is made from the reaction
of hexamethylenediamine and adipic acid, as shown in the following
equation:

Hexamethylenediamine

Adipic acid

Poly(hexamethylene adipamide)
(nylon-6,6)

(2)

For a molecule to be a monomer, it must be at least bifunctional. The
functionality of a molecule refers to its interlinking capacity, or the
number of sites it has available for bonding with other molecules.
Reactions between monofunctional molecules use up the reactive groups
completely and render the product incapable of further reactions,
whereas the presence of two condensable groups in both hexamethylenediamine (-NH2) and adipic acid (-COOH) makes each of these
monomers bifunctional with the ability to form polymers. In this respect,
styrene is also a bifunctional monomer because the extra pair of electrons in the double bond can form two bonds with vinyl groups in other
molecules.
The number of repeating units in the polystyrene structure (1) is indicated by the index n. This is known as the degree of polymerization

(DP). It specifies the length of the polymer chain. Oligomer is a very low


Figure 14.1 Schematic structure of fully stretched polyethylene.

molecular weight polymer usually with less than 10 repeating units. The
word oligomer is derived from the Greek word oligos meaning a few.
Oligomers exhibit different thermal and mechanical properties compared to the corresponding high-molecular weight polymer. It is sometimes useful to prepare oligomers with certain functional groups at the
end that can be used in further chemistry. The degree of polymerization
represents one way of quantifying the molecular weight or size of a
polymer. For example, a linear polyethylene consisting of one thousand
ethylene units will have a molecular weight of 28,000, and an extended
length of 2520 angstroms (A) (Fig. 14.1). However, because of rotation
of the carbon-carbon bonds, the polymer chains are seldom extended to
their full contour length but are present in many different shapes or conformations.
14.2

Classification of Polymers

Polymers can be classified in many ways according to various criteria
such as:
a. Origin of the polymer: Polymers can be classified as being natural or synthetic based on the origin of the polymer. Certain polymers, such as nucleic acids, proteins, cellulose, natural rubber, wool,
and silk are found in nature. Clays, sands, graphite, and diamond are
also naturally occurring polymers. On the other hand, thousands of
polymers have been synthesized and more are likely to be produced
in the future. In some cases, naturally occurring polymers can be produced by synthetic routes. For example, polyisoprene is the synthetic
version of natural rubber (Hevea).
b. Functional groups present in the repeating unit: In this respect,
polymers can be grouped in families like polyesters, polyamides,
polyimides, polycarbonates, polyurethanes, polyureas, polyethers,

polysulfides, and so on.
c. Polymer structure: A polymer can be described as:
1. Linear, branched, cross-linked, ladder, star-shaped, combshaped, dendritic, and the like (Fig. 14.2)


linear

branched

comb

star

crossl inked
(network)

ladder

dendritic

Figure 14.2 Schematic representation of different polymer structures.

2. Amorphous or crystalline based on absence or presence of longrange ordered pattern among polymer chains
3. Homopolymer or copolymer with different types of copolymer
4. Fibers, plastics, or elastomers. Polymers (synthetic or natural)
can be divided into various families; fibers, elastomers, plastics,
adhesives, and each family itself has subgroups
d. Polymerization mechanism: Based on the polymer-forming reaction; condensation versus addition or step-growth versus chaingrowth polymerization reactions
e. Preparative technique: Bulk, solution, suspension, emulsion, or
precipitation

/. Thermal behavior: Thermoplastics or thermosets
g. End use: Such as diene polymers (rubber industry); olefin polymers (sheet, film, and fiber industries); and acrylics (coating and
decorative materials)


Tension

Random
Release of
Oriented
coil
tension
(b)
(a)
Figure 14.3 Illustration of rubbery elastomeric property,
(a) Relaxed: high entropy; (b) Stretched: low entropy.

Elastomers. Elastomers are polymeric materials with irregular structure and weak intermolecular attractive forces. Elastomers are capable
of high extension (up to 1000%) under ambient conditions. That is, they
have the particular kind of elasticity characteristic of rubber. The elasticity is attributed to the presence of chemical and/or physical crosslinks
in these materials. In their normal state, elastomers are amorphous, and
as the material is stretched, the random chains are forced to occupy more
ordered positions. Releasing the applied force allows the elongated
chains to return to a more random state. Thus, the restoring force after
elongation is largely because of entropy. (Fig. 14.3)
In addition to natural rubber, there are synthetic elastomers such as
diene elastomers (e.g., polybutadiene, polyisoprene, polychloroprene,
and so on,), nondiene elastomers (e.g., polyisobutylene, polysiloxanes,
polyurethanes), and nitrile and butyl rubber. Elastomers can also be
made from block copolymers containing hard or rigid segments of

polyurethane and soft or flexible segments derived from the polyester
or polyether diols with degrees of polymerization generally above 15.
Polyurethane elastomeric materials exhibit good abrasion resistance,
chemical resistance, and good tear strength with a wide variation of flexibility available. These polyurethanes are also used in fabrics and sporting goods. (Fig. 14.4)
Fibers. A fiber is often defined as an object with a length-to-diameter
ratio of at least 100. Fibers (synthetic or natural) are polymers with high
molecular symmetry and strong cohesive energies between chains that
usually result from the presence of polar groups. Fibers possess a high
degree of crystallinity characterized by the presence of stiffening groups
in the polymer backbone, and of intermolecular hydrogen bonds. Also,
they are characterized by the absence of branching or irregularly spaced


Isoprene

Polyether or
polyester

cis-1,4-polyisoprene
(natural rubber)

Aromatic diisocyanate
(excess)

(unreacted)

hard segment

soft segment

Figure 14.4 Examples of synthetic elastomers, (a) polyisoprene, and (6) polyurethane
elastomer.

pendant groups that will otherwise disrupt the crystalline formation.
Fibers are normally linear and drawn in one direction to make them
long, thin, and threadlike, with great strength along the fiber. These
characteristics permit formation of this type of polymer into long fibers
suitable for textile applications. Typical examples of fibers include polyesters, nylons, and acrylic polymers such as polyacrylonitrile, and naturally occurring polymers such as cotton, wool, and silk. (Fig. 14.5)
Plastics. Plastics are the polymeric materials with properties intermediate between elastomers and fibers. In spite of the possible differences in chemical structure, the demarcation between fibers and plastics
may sometimes be blurred. Polymers such as polypropylene and
polyamides can be used as fibers and plastics by a proper choice of processing conditions. Plastics can be extruded as sheets or pipes, painted
on surfaces, or molded to form countless objects. A typical commercial
plastic resin may contain two or more polymers in addition to various
additives and fillers. Additives and fillers are used to improve some
property such as the processability, thermal or environmental stability,
and mechanical properties of the final product.
Thermoplastics and thermosets. All polymers can be divided into two
major groups {thermoplastics and thermosets) based on their thermal processing behavior. Thermoplastic polymers soften and flow under the action


Poly(ethylene terephthalate)
(polyester)

Hexamethylenediamine

Sebacoyl chloride

Acrylonitrile

Poly(hexamethylsebacamide)

(nylon-6,10)

Poly(acrylo nitrile)

Figure 14.5 Examples of synthetic fibers: polyester, nylon and poly (acrylonitrile).

of heat and pressure. Upon cooling, the polymer hardens and assumes the
shape of the mold (container). Thermoplastics, when compounded with
appropriate ingredients, can usually withstand several heating and cooling cycles without suffering any structural breakdown. Examples of commercial thermoplastics are polystyrene, polyolefins (e.g., polyethylene
and polypropylene), nylon, poly(vinyl chloride), and poly(ethylene
terephthalate) (Fig. 14.6). Thermoplastics are used for a wide range of

Ethylene

Polyethylene

Propylene

Polypropylene

Vinyl chloride

Poly(vinyl chloride)

Figure 14.6 Examples of commercial thermoplastics.


applications, such as film for packaging, photographic, and magnetic
tape, beverage and trash containers, and a variety of automotive parts
and upholstery. Advantageously, waste thermoplastics can be recovered

and refabricated by application of heat and pressure.
Thermosets are polymers whose individual chains have been chemically linked by covalent bonds during polymerization or by subsequent
chemical or thermal treatment during fabrication. The thermosets usually exist initially as liquids called prepolymers; they can be shaped
into desired forms by the application of heat and pressure. Once formed,
these cross-linked networks resist heat softening, creep and solvent
attack, and cannot be thermally processed or recycled. Such properties
make thermosets suitable materials for composites, coatings, and adhesive applications. Principal examples of thermosets include epoxies,
phenol-formaldehyde resins, and unsaturated polyesters. Vulcanized
rubber used in the tire industry is also an example of thermosetting polymers. Thermosetting polymers are usually insoluble because the
crosslinking causes a tremendous increase in molecular weight. At most,
thermosetting polymers only swell in the presence of solvents, as solvent molecules penetrate the network. Examples of the reactions of
phenol and formaldehyde to yield phenol-formaldehyde resins are shown
in Fig. 14.7.
Properties of a specific polymer can often be varied by means of controlling molecular weight, end groups, processing, cross-linking, additives, and so on. Therefore, it is possible to classify a single polymer in
more than one category. For example, nylon can be produced as fibers
in the crystalline forms, or as plastics in the less crystalline forms. Also,
poly(vinyl chloride) and siloxanes can be processed to act as plastics or
elastomers.
Commodity and engineering polymers. On the basis of end use and economic considerations, polymers can be divided into two major classes:
commodity plastics and engineering polymers. Commodity plastics are
characterized by high volume and low cost. They are used frequently in
the form of disposable items such as packaging film, but also find application in durable goods. Commodity plastics comprise principally of
four major thermoplastic polymers: polystyrene, polyethylene, polypropylene, and poly (vinyl chloride).
Engineering plastics refer to those polymers that are used in the manufacture of premium plastic products where high temperature resistance,
high impact strength, chemical resistance, or other special properties
are required. They compete with metals, ceramics, and glass in a variety of applications. Engineering plastics are designed to replace metals.
Compared to commodity plastics, engineering plastics are specialty polymers that provide outstanding properties such as superior mechanical


heat

Phenol

Formaldehyde

(a) Novolac

(b) Resole

Figure 14.7 Representative structures of phenol-formaldehyde resins: (a) novolac (formed
under acidic conditions), and (b) resole (formed under basic conditions).


properties, high thermal stability, excellent chemical resistance, low
creep compliance, and high tensile, flexural, and impact strength. In contrast to commodity plastics, however, engineering and specialty polymers are produced at lower volume and higher cost. Examples of
engineering plastics include aliphatic polyamides (such as nylon-6,6),
aromatic polyamides, acrylonitrile-butadiene-styrene (ABS) resin, polyacetal, polycarbonate, polysulfones, poly(phenylene oxide) resins,
poly(phenylene sulfide), and fluoroplastics such as teflon. Structures of
some of these polymers are shown in Fig. 14.8.
Specialty polymers achieve very high performance and find limited but
critical use in aerospace composites, in electronic industries, as membranes for gas and liquid separations, as fire-retardant textile fabrics
for firefighters and race-car drivers, and for biomedical applications (as
sutures and surgical implants). The most important class of specialty
plastics is polyimides. Other specialty polymers include polyetherimide,
poly(amide-imide), polybismaleimides, ionic polymers, polyphosphazenes,
poly(aryl ether ketones), polyarylates and related aromatic polyesters,
and ultrahigh-molecular-weight polyethylene (Fig. 14.9).
14.3

Polymers Industry

Today, polymeric materials are used in nearly all areas of daily life that
it is right to claim that we live in a polymer age. The evidence is all
around us. Polymers are used in shelter, clothing, health, food, transportation, and almost every facet of our lives. In fact, it is hard to imagine what the world would be like without synthetic polymers. Production
and fabrication of polymers are major worldwide industries. The data
presented in Tables 14.1 to 14.8 indicate the size of the polymers' marketplace in the 1992 to 2002 decade [I].
14.4

Polymer Structure

The properties of polymers are strongly influenced by details of the
chain structure. The structural parameters that determine properties
of a polymer include the overall chemical composition and the sequence
of monomer units in the case of copolymers, the stereochemistry or tacticity of the chain, and geometric isomerization in the case of diene-type
polymers.
Homopolymer. It is a macromolecule consisting of only one type of
repeating unit. The repeating unit may consist of a single species as in
PS (1), or may contain more species of monomer unit. Polymers such as
nylon-6,6 (2) that have repeating units composed of more than one
monomer are considered homopolymers.


Terephthaloyl chloride

p-phenylenediamine

Poly(p-phenylene terephthalamide)
(Kevlatr™)

Isophthaloyl chloride

m-phenylenediamine

Poly(m-phenylene isophthalamide)
(Nomex™)

Phosgene

Polycarbonate

Bisphenol-A

catalyst

Poly(2,6-dimethyl-l ,4-phenylene oxide)

2,6-xylenol

Polyethersulfone
(Ultrason E™, Victrex™)

/?-dichlorobenzene

Tetrafluoroethylene

Figure 14.8

Sodium sulfide

Poly(/?-phenylene sulfide)

Polytetrafluoroethylene
(Teflon™)

Examples of engineering plastics.

Copolymer. It is a macromolecule consisting of more than one type of
building unit or mer. Copolymerization will be discussed in Sec. 14.10.
Head-to-head vs. head-to-tail. Substituted vinyl monomers can join in one
of two arrangements; head-to-tail or head-to-head configurations


Pyromellitic anhydride

4,4-diamino diphenyl ether

(polyimide) Polypyromellitimide
(Kapton®)

Potassium salt of hydroquinone

4,4'-difluorobenzophenone

Polyetheretherketone
(PEEK,Victrex®)

Figure 14.9 Examples of specialty polymers.

(Fig. 14.10). Due to steric and electronic considerations, the usual
arrangement is head-to-tail, so that the pendant groups are usually on

every other carbon atom in the chain.
Linear polymers. A linear polymer is a polymer molecule in which the
atoms are more or less arranged in a long chain called the backbone. This
is best illustrated with the structure of polyethylene (Fig. 14.1). However,
polymers such as polypropylene or poly(l-pentene) in which a small
chain called pendant groups presents in the repeating unit, are also
designated as a linear polymer. The chains of pendant groups are much


TABLE 14.1

U.S. Plastics and Synthetic Rubber
U.S. Plastics
Production (Thousands of metric tons3)
1992

Thermoplastic resins
Polyethylene
Low densityb'c
Linear low densitybc
High densitycd
Polypropylene6
Styrene polymers
Polystyrenef
Styrene-acrylonitrileg
Acrylonitrilebutadiene-styrene
and other styrene
polymersgh
Polyamine, nylon type
Polyvinyl chloride and

copolymers6
Total
Thermosetting resins
Epoxy1
Urea and melamine
Phenolic
Total
Grand Total, Plastics

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

3,299

2,106
4,449
3,820

3,278
2,196
4,509
3,914

2,077
2,278
5,043
4,327

3,467
2,378
5,085
4,940

3,531
2,885
5,612
5,439

3,489
3,124
5,696
6,042

3,437

3,278
5,862
6,271

3,493
3,677
6,289
7,028

3,436
3,607
6,336
7,139

3,491
4,659
6,933
7,228

3,647
5,139
7,243
7,691

2,312
51
1,184

2,442
48

1,326

2,653
63
1,465

2,566
59
1,319

2,751
55
1,347

2,894
44
1,359

2,829
55
1,447

2,935
56
1,406

3,104
58
1,415

2,773
58
1,240

3,025
59
1,323

303
4,531

348
4,652

428
5,312

463
5,577

500
5,996

554
6,388

583
6,578

612

6,764

581
6,551

517
6,467

578
6,939

22,055

22,713

23,644

25,853

28,117

29,590

30,341

32,259

32,227

33,365

35,644

207
807
1,326
2,341

232
914
1,396
2,542

287
955
1,453
2,695

290
1,302
1,787
3,379
33,720

298
1,354
1,990
3,642
35,901

314
1,437
1,974
3,726

273
1,379
1,979
3,630

25,255

300
1,104
1,577
2,981
31,098

297
1,197
1,694
3,187

24,396

273
1,005
1,465
2,742
26,386

35,953

36,995

297
1,460
2,013
3,770
39,414

910
588
339
88
66
478
2,469

874
605
349
89
64
484
2,465

782
562
306

84
57
424
2,215

768
583
301
84
54
425
2,215

28,548

32,777

U.S. Synthetic Rubbers
Styrene-butadiene rubber
Polybutadiene
Ethylene-propylene
Nitrile, solid
Polychloroprene
Otherj
Total

796
465
207
74

72
381
1,995

817
473
227
78
70
400
2,065

851
505
262
84
76
408
2,186

878
523
270
83
70
427
2,251

907
535

289
85
70
437
2,323

932
564
309
85
73
449
2,412

908
561
320
87
69
447
2,392

NOTE: Totals for plastics are for those products listed and exclude some small-volume plastics. Synthetic rubber data include Canada. aDry-weight basis unless otherwise specified;
Density 0.940 and below; cData include Canada from 2001; dDensity above 0.940; eData include Canada from 1995; fData include Canada from 2000; BData include Canada from 1994;
Includes styrene-butadiene copolymers and other styrene-based polymers; "Unmodified; includes butyl styrene-butadiene rubber latex, nitrile latex, polyisoprene, and miscellaneous others.
SOURCES: American Plastics Council, International Institute of Synthetic Rubber Producers.

b

h

TABLE 14.2 Canada Plastics
Production (Thousands of metric tonsa)

Polyesters, unsaturated
Polyethylene41
Polystyrene13

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

40
1660
167

45
1742
158

60
1908
177

58
2073
189

61
2194
209

71
2195
181

82
2283
180

108

2485
200

120
2751
203

115
3035
186

113
3330
195

includes high-, low-, and linear low-density polyethylene; includes acrylonitrile-butadiene-styrene.
SOURCE: Statistics Canada.


TABLE 14.3 Europe Plastics and Synthetic Rubber
Production (Thousands of metric tons)

Polyethylene
Polystyrene
Acrylonitrile-butadienestyrene
Polyvinyl chloride
Epoxy resins
Polypropylene
Polyamides
Synthetic rubber

a

1995

1996

1997

1998

1999

2000

2001

2002a

2,832
891
643
3,905
340
NA
441
1,753

3,000
1,044
604

4,322
282
NA
843
1,946

8,508
1,117
762
4,792
373
NA
1,652
2,419

9,731
1,090
859
2,651
334
4,158
1,494
2,245

10,223
675
971
3,209
393
6,524

766
2,239

10,579
331
1,038
4,893
419
6,984
1,412
2,342

5,481
592
466
3,902
89
5,644
1,209
2,691

4,778
764
121
3,792
54
3,380
616
2,068

C&EN estimates based on partial reporting; NA = not available.
SOURCES: European Union and national government statistics offices, EuroChlor, Association of Petrochemicals Producers in Europe.


TABLE 14.4 Asia Plastics and Synthetic Rubber
In Japan
Production (Thousands of metric tons)

Polyethylene, low-density
Polyethylene, high-density
Polyethylene terephthalate
Polypropylene
Polyvinyl chloride
Polystyrene
Epoxy
Phenolic resins
Polycarbonate
Synthetic rubber

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

NA
NA
NA
2038
1981
2005
NA
356
NA
1388

1573
1024
1213
2031
1980
1966
170
328

149
1310

1645
1113
1279
2225
2112
2099
181
330
171
1349

1748
1238
1377
2502
2274
2149
194
327
227
1498

1830
1271
1360
2730
2511

2178
201
294
251
1520

1839
1313
1398
2854
2626
2201
222
303
292
1592

1760
1168
1300
2520
2457
1975
204
259
317
1520

1856
1301

1281
2626
2460
2037
225
250
351
1577

1892
1246
1308
2721
2410
2024
243
262
354
1590

1852
1240
1243
2696
2195
1810
192
232
370
1466

1789
1181
1211
2641
2225
1837
201
242
386
1522

Na = not available.
SOURCE: Ministry of Economy, Trade & Industry.
In South Korea
Production (Thousands of metric tons)

Acrylonitrile-butadiene-styrene
Polyethylene, low-density
Polyethylene, high-density
Polypropylene
Polystyrene
Polyvinyl chloride

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

310
761
1019
1223
754
726

350
853
1189
1436
809
760

409
923
1294
1607
869
791

491
970
1232
1619
905
914

560
1256
1340
1738
1000
1005

596
1394
1549
2056
1104
1087

636
1518

1615
2355
1038
1013

784
1642
1756
2440
1105
1170

111
1576
1706
2413
1185
1191

858
1614
1839
2422
1224
1238

1,055
1620
1868
2622

1361
1221

SOURCE: National Statistical Office, Republic of Korea.


In Taiwan
Production (Thousands of metric tons)

Acrylonitrile butadiene-styrene
Polyethylene, low-density
Polyethylene, high-density
Polyester filament
Polypropylene
Polystyrene
Polyvinyl chloride
Synthetic rubber
Styrene-butadiene
Polybutadiene

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

569
211
149
903
225
528
1043

642
217
152
1033
220
593
1078

742
224

188
1179
341
626
1114

757
214
212
1249
417
671
976

911
233
241
1298
448
808
1105

979
235
243
1429
420
790
1149

901
224
275
1615
418
784
1158

1020
236
395
1671
515
784
1397

1059
243
306
1632
561
748
1387

982
472
507
1584
751
911

1434

1077
411
513
1603
831
892
1484

64
45

65
43

152
46

161
52

157
51

167
55

173
56

175
55

159
51

174
53

173
66

SOURCE: Taiwan Ministry of Economic Affairs.


TABLE 14.5

China Plastics and Synthetic Rubber

Production (Thousands of metric tons)

Plastics
Polyvinyl chloride
Polyethylene
Polypropylene
Polyester fiber
Synthetic rubber

1997

1998

1999

2000

2001

2002

6474
1536
2152
1881
1274
623

7029
1599
2292
2075
2503
589

8418
1894
2714
2722
1898

761

10,794
2397
3000
3239
2210
836

12,038
2877
3122
3225
2932
1045

13,665
3389
3547
3742
3139
1168

SOURCE: China National Chemical Information Center.

smaller than the backbone chain, which usually has hundreds of thousands of atoms.

l-pentene

PoIy(I-pentene)

Branched polymers. In branched polymers (Fig. 14.2), chain extensions
or branches are present on branch points, irregularly spaced along the
polymer chain. The number of branches in nonlinear polyethylene (lowdensity polyethylene, LDPE) may vary from 1.5 per 20 methylene groups
to 1 per 2000 methylene groups. This branching increases the specific
volume and thus reduces the density of the polymer.

head-to-tail
head

tail

head-to-head

tail-to-tail

Styrene
Figure 14.10 Illustration of head-to-tail and head-to-head configurations.


TABLE 14.6

U.S. Paints and Coatings

Shipments (Millions of liters)

Architectural
Product
Special purpose
Total

a

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2180
1181
655
4016

2301

1351
678
4330

2441
1412
734
4587

2350
1423
738
4512

2422
1510
791
4724

2483
1609
689
4780

2392
1620
655
4667

2498

1665
659
4822

2464
1715
689
4868

2339
1540
613
4493

2566
1567
590
4724

For original equipment manufacturers.
SOURCE: Department of Commerce.


TABLE 14.7 U.S. Synthetic Fibers
Production (Thousands of metric tons)
1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

Noncellulosic fibers
Acrylica
Nylon
Olefin
Polyester
Total

199
1159
894
1622
3874

196
1206
959
1613
3975

200
1243
1083
1750
4276

196
1226
1085
1763
4270

211
1270
1095
1736
4311

209
1286
1216
1855
4567

157
1218
1326
1768
4469

143
1217
1395
1736
4491

154
1215
1461
1775
4605

137
1019
1342
1456
3954

150
1106
1352
1471
4080

Cellulosic fibers
Acetateb and rayon
Total fibers

225
4099

229
4204

227
4503

226
4496

215
4527

208
4775

166
4635

134
4625

158
4764

103
4057

81
4160

a

Includes modacrylic; includes diacetate and triacetate; excludes production for cigarette filters.
SOURCE: Fiber Economics Bureau.


TABLE 14.8 Europe Synthetic Fibers
Production (Thousands of metric tons)

Acrylic
Polyester
Polyamide
Cellulosics

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

745
955
650
713

686
895
591
713

714
982
641
682

623
973

632
736

677
895
632
766

705
995
673
722

650
959
641
715

614
909
595
651

623
968
636
627

842
1472

708
457

861
1480
698
450

SOURCE: International Rayon & Synthetic Fibers Committee.


Cross-linked polymers. In cross-linked polymer systems (Fig. 14.2), polymer chains become chemically linked to each other resulting in a network. Network structures are formed when the average functionality of
a mixture of monomers is greater than 2. Network polymers can also be
made by chemically linking linear or branched polymers. For example,
in a tire, the rubber polymer chains are interconnected with sulfur linkages in a process called vulcanization (Fig. 14.11).
Both linear and branched polymers are thermoplastics. However,
cross-linked three-dimensional, or network-polymers are thermoset polymers. The cross-linked density may vary from the low cross-linked density in vulcanized rubber to high cross-linked density observed in ebonite
(hard rubber; highly cross-linked natural rubber).
Ladder polymers. A ladder polymer consists of two parallel linear strands
of molecules with a regular sequence of cross-links. Ladder polymers
have only condensed cyclic units in the chain. The molecular structure
of ladder polymers is more rigid than that of conventional liner polymers.
Typical examples of ladder polymers are shown in Fig. 14.12.

Figure 14.11 Vulcanization of polybutadiene.


Poly(acrylo nitrile)

oxidation

(removal of H2)

Figure 14.12

Examples of ladder polymers.


Star-shape polymers. Star polymers contain three or more polymer
chains emanating from a central structural unit (Fig. 14.2).
Comb polymers. Comb polymers contain pendant chains (which may or
may not be of equal length) and are related structurally to graft copolymers. Such a polymer might be formed, for example, by polymerizing a
long-chain vinyl monomer (i.e., macromonomer).
Tacticity. In addition to the type, number, and sequential arrangement
of monomers along the chain, tacticity or the spatial arrangement of substituent groups is also important in determining properties. Three types
of steric configurations are possible from polymerizing asymmetric vinyl
monomers, as represented with polypropylene in Fig. 14.13:
1. All the methyl groups could be protruding from the chain in a random
fashion; this is named an atactic polymer.
2. The methyl groups could alternate from one side of the chain to the
other; this is called a syndiotactic polymer.
3. The methyl groups could all be on the same side; then the polymer
is said to be isotactic polymer.
Because of their orderly arrangements, the chains of the tactic polymers (syndiotactic and isotactic) can lie closer together and the polymers
are partially crystalline, whereas atactic polymers are amorphous and
soft indicating the absence of all crystalline order. Isotactic polypropylene is highly crystalline with a melting point of 1600C, whereas the atactic isomer is an amorphous (noncrystalline) soft polymer with a melting

Atactic:

Syndiotactic:

Isotactic:
Figure 14.13 Three types of polypropylene.


point of 75°C. In addition to crystallinity, other polymer properties, such
as thermal and mechanical behavior, can be significantly affected by the
tacticity of the polymer.
Until 1953, most addition polymers were made by free-radical paths,
which produce atactic polymers. In that year, however, the Nobel laureates Karl Ziegler and Giulio Natta introduced a new technique for
polymerization using a type of catalyst that permits control of the
stereochemistry of a polymer during its formation.
Geometric isomerism. When there are unsaturated sites along a polymer chain, several different isomeric forms are possible. As illustrated
in Fig. 14.14, conjugated dienes such as isoprene and chloroprene can
be polymerized to give either 1,2-, 3,4, or 1,4-polymer. In the case of 1,4polymers, both cis and trans configurations are possible. Also, stereoregular (i.e., isotactic and syndiotactic) polybutadienes can be produced
in case of 1,2- and 3,4-polymerization.
It is possible to control the type of polymer produced. This is best
illustrated with polymerization of the monomer isoprene; 2-methyl-l,3butadiene. The Ziegler-Natta catalyst, consisting of a titanium tetrachloride

trans- 1,4-polymer

1,2-polymer

3,4-polymer

ds-1,4-polymer

R

Monomer

Polymer

H
Cl
CH3

1,3-butadiene
2-chloro-1,3-butadiene
2-methyl-1,3-butadiene

polybutadiene
polychloroprene
polyisoprene

Figure 14.14 Possible polymer structures from the polymerization of
conjugated dienes.